The influence of OH groups in [Fe(CO)3]2[(μ- ECH2)2C(CH2OH)2] (E = S, Se) complexes toward the cathodic process

Article abstract of DOI:10.1002/zaac.201300106

[FeFe] hydrogenase model complexes [Fe(CO)₃]₂[(μ- ECH₂)₂C(CH₂OH)₂] (E = S (1) or Se (2)) containing CH₂OH bridgehead substituents were synthesized via reaction of equimolar amounts of 4, 4-bis(hydroxymethyl)-1, 2-dithiolane (A) or 4, 4-bis(hydroxymethyl)-1, 2-diselenolane (B) with Fe₃(CO) ₁₂ in toluene at 100°C. The presence of OH groups in complexes 1 and 2 is found to influence the cathodic processes and their potentials. The catalytic reduction of acetic acid (AcOH) occurs by the anions 1^- and 2^-, while the neutral complexes are procatalysts. Copyright

Full text of DOI:10.1002/zaac.201300106

ARTICLE
DOI: 10.1002/zaac.201300106
The Influence of OH Groups in [Fe(CO) ] [(μ-ECH ) C(CH OH) ]
3
2
2 2
2
2
(
E = S, Se) Complexes toward the Cathodic Process
[a]
[a]
[a]
[a,b]
Ralf Trautwein, Laith R. Almazahreh, Helmar Görls, and Wolfgang Weigand*
Keywords: Iron; Hydrogenases; Hydrogen bonding; Electrochemistry; Selenium
Abstract. [FeFe] hydrogenase model complexes [Fe(CO)
3
]
2
[(μ- presence of OH groups in complexes 1 and 2 is found to influence the
cathodic processes and their potentials. The catalytic reduction of ace-
ECH C(CH OH) ] (E = S (1) or Se (2)) containing CH OH bridge-
2
)
2
2
2
2
–
–
head substituents were synthesized via reaction of equimolar amounts tic acid (AcOH) occurs by the anions 1 and 2 , while the neutral
of 4,4-bis(hydroxymethyl)-1,2-dithiolane (A) or 4,4-bis(hydroxy- complexes are procatalysts.
3
methyl)-1,2-diselenolane (B) with Fe (CO)12 in toluene at 100 °C. The
In all of the reported Fe FeI complexes of the type
I
Introduction
–
Fe (μ-SR) (CO) L [L = PR , SR , CN , NCN (carbenes),
2
2
6–n
n
3
2
Nature catalyzes the production of hydrogen with high effi-
ciency and low energy features through [FeFe] hydrogenase
n = 0–4], the CO ligands are in a terminal position. The rotated
structure with bridging CO ligand has been detected for the
reduced complexes with silicon , sulfur and selenium
bridgehead atoms as well as for [Fe(CO) ] [(μ-1,2-benzenedi-
thiolato)] . In addition, some oxidized complexes adopting
the rotated structure are the nitrosyl-substituted diiron dithiol-
and {[Fe(CO) PMe ][Fe(CO) NHC][(μ-
2 3 2
SCH ) CR )]} . Moreover, the rotated structure has been
calculated for the cationic species of the complexes containing
sulfur and selenium bridgehead atoms as well as for
[Fe(CO) ] [(μ-1,2-benzenedithiolato)]} . In total picture,
two factors, the steric and the electronic, are responsible for
stabilizing the reduced and oxidized states: (i) The steric inter-
action between the bulky bridgehead groups and the apical CO
[
1–4]
showing a [Fe S ] cluster in its active site.
Inspired by
2
3
[6]
[7]
[7]
these properties, there has been a great impetus to scientists
for paving the way to design a cheap and robust electrocatalyst
that mimics the structure of the active site. The activity of the
3
2
[8]
+
–
enzyme in catalyzing the interconversion 2H + 2e ↔ H is
2
[10]
ato complexes
attributed to a structural feature, so called rotated structure,
+
[8]
which offers a vacant site at the distal FedI in the reduced
2 2
2
[
5]
Hred and the oxidized Hox states (Figure 1). The catalytic
[7]
[7]
+
formation of H requires interaction of H at the vacant site of
2
+[9]
{
3 2
Hred and the oxidation of dihydrogen occurs catalytically
through binding at the vacant site of H . Thus, any successful
synthetic model catalyst must possess a vacant coordination
site or must be able to generate it during the catalytic cycle.
ox
lowers the rotational barrier of the Fe(CO) moiety. (ii) Higher
3
electron density at the iron atom due to strong electron donat-
ing groups such as PMe and carbenes, respectively, favors the
3
formation of a bridging CO ligand in the reduced and the oxid-
ized forms, respectively.[ The rotated structures of cationic
complexes with sulfur or selenium bridgehead atoms are stabi-
lized by the interaction between the lone pair of the bridgehead
atom and the inverted iron atom. Additionally, the influence of
H-bonding toward the stability of the reduced species has also
been studied in [Fe(CO) ] [(μ-1,2-hydroquinonedithiolato)]
11]
Figure 1. Structures of the active site in the Hox and Hred states. Fe
and Fe are distal and proximal iron atoms, respectively, with respect
to the [Fe ] cluster.
d
3
2
p
and related structures.[
12]
4 4
S
Herein, we describe the synthesis of the model complexes
*
Prof. Dr. W. Weigand
[Fe(CO) ] [(μ-ECH ) C(CH OH) ] (E = S (1) or Se (2)). We
3
2
2 2
2
2
E-Mail: wolfgang.weigand@uni-jena.de
discuss the influence of replacement of the alkyl bridgehead
[
[
a] Institut für Anorganische und Analytische Chemie
Friedrich-Schiller-Universität Jena
Humboldtstrasse 8
1
2
substituents in the complexes [Fe(CO)
]
[(μ-SCH
) CR R ]
3
2
2 2
1
2
[13]
(R /R = Me/Me, Et/Et, Bu/Et)
by CH OH in complexes 1
2
07743 Jena, Germany
and 2 with respect to the mechanism of the cathodic process
and the reduction potentials of the model complexes. More-
over, we study the electrochemical behavior of complexes 1
and 2 in the presence of acetic acid (AcOH) at various concen-
trations.
b] Jena Center for Soft Matter (JCSM)
Philosophenweg 7
0
7743 Jena, Germany
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201300106 or from the au-
thor.
1
512
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 639, (8-9), 1512–1519

3 2 2 2 2 2
Influence of OH Groups in [Fe(CO) ] [(μ-ECH ) C(CH OH) ] (E = S, Se) Complexes
Results and Discussion
a singlet at δ = 2.38 ppm due to the CH
2
S protons, a doublet
3
centered at δ = 3.39 ppm for the CH O ( J
= 4.9 Hz) and a
2
H,H
3
Synthesis
triplet centered at δ = 4.05 ppm owing to the OH protons ( J
H,H
1
=
5.2 Hz). In the H NMR spectrum of complex 2, the protons
Treatment of Fe (CO) with compound A[14] or B[15] in
3
12
77
of CH S, CH O and OH resonate at 2.44 (singlet with Se
2
2
toluene at 100 °C for one hour followed by column chromatog-
raphy afforded complexes 1 and 2 in 45% and 41% yields,
respectively (Scheme 1). We synthesized compound A accord-
ing to Scheme 2.
2
3
satellites, J
= 19.0 Hz), 3.40 (doublet with J
= 4.8 Hz)
H,H
Se,H
3
and 4.04 (triplet with J
= 5.0 Hz) ppm, respectively. The
H,H
13
1
C{ H} NMR spectrum of complex 1 shows four singlets at
23.4, 43.5, 65.3 and 208.9 ppm attributing to the carbon atoms
of CH S, the quaternary bridgehead atom, CH O and the carb-
2
2
onyl carbon atoms, respectively. In the 13C{ H} NMR spec-
1
trum of complex 2, the carbon atoms of the CH Se groups
2
resonate at δ = 16.2 ppm as singlet with 77Se satellites, ( J
1
Se,C
=
83 Hz). The spectrum shows also a singlet at δ = 42.8 ppm
for the bridgehead carbon atom and additional signals for the
carbon atoms of the CH O and Fe(CO) moieties at 64.6 and
Scheme 1. Synthesis of complexes 1 and 2.
2
3
1
77
209.7 ppm, respectively. The H Se HMBC NMR spectrum
of complex 2 displays a singlet at δ = 74.5 ppm for the selen-
ium atoms.
Molecular Structures
Scheme 2. Synthesis of compound A: (i) toluene/acetone, H
3
PO
2
4
, re-
Single crystals suitable for X-ray diffraction studies were
obtained by diffusion of pentane into a concentrated benzene
solution of complex 1 or 2 at room temperature. Molecular
structures and numbering schemes of the complexes are shown
in Figure 2. As can be seen in Figure 2, each iron center in 1
or 2 adopts a distorted octahedral geometry with three facial
CO ligands, one iron atom and two bridging sulfur atoms with
15]
flux, 16 h[ (ii) EtOH, Na
[14]
2
S
2
, reflux, 4 h
(iii) EtOH/H O, HCl,
room temperature, 24 h. The detailed procedure of step (iii) is pre-
sented in the Experimental Section.
Spectroscopic Characterization
1
13
1
Complexes 1 and 2 were characterized by H, C{ H} and cis-fashion. The bicyclic [Fe S ] structure in these complexes
2
2
1H Se HMBC (for complex 2) NMR as well as IR spec- reveals butterfly conformation. The bridgehead carbon atom is
77
troscopy, MS spectrometry, elemental analysis and X-ray crys- surrounded in a distorted tetrahedral environment.
tallography. The MS spectra of complexes 1 and 2 reveal the
parent ion peaks at m/z = 418 and 512 [M – CO] , respec- shorter than that in complex 2 [2.5473(7) Å] because of the
tively, and a stepwise fragmentation with the loss of five CO smaller size of sulfur compared to that of selenium.
The Fe–Fe bond length in complex 1 [2.5006(5) Å] is
+
[
7,17]
The
groups. In the IR spectrum of complex 1 (Figure S1 and S2), Fe–Fe bond lengths in both complexes are shorter than those
the CO absorptions bands (2072, 2022, 2001, 1985, 1980, of the active site, 2.55–2.62 Å[ , but within the range of the
18]
–
1
1
961 cm ) are shifted to higher wavenumbers compared to previously reported model complexes. Interestingly, the
those of complex 2 (2062, 2013, 1993, 1972, 1968, average C–C–S angle in complex 1 (121.1°) and the average
–
1
1
951 cm ) (Figures S3 and S4). These shifts indicate in- C–C–Se angle in complex 2 (121.7°) are larger than those
[
19]
creased electron density at the diiron core when sulfur is re- found in model complexes with carbon bridgehead atoms
,
placed by selenium being consistent with the different electro- but comparable to those in complexes containing silicon and
negativities.[
7,16]
The H NMR spectrum of complex 1 exhibits tin bridgehead heteroatoms
1
[6,20]
. The molecular packings of
Figure 2. Molecular structures (50% probability) of complexes 1 (left) and 2 (right). Hydrogen atoms were omitted for clarity.
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Z. Anorg. Allg. Chem. 2013, 1512–1519
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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R. Trautwein, L. R. Almazahreh, H. Görls, W. Weigand
ARTICLE
Figure 3. Molecular packing of 2. Hydrogen atoms were omitted for clarity. Left: View along the axis of the [OH]
4
tetrahedra. Right: Rotated
by 90°. Linear arrangement of two different distorted [OH]
4
tetrahedra I and II in alternating order. Tetrahedron I: dO···O = 3.19 and 2.85 Å;
tetrahedron II: dO···O = 3.11 and 2.87 Å.
compounds 1 (Figure S5) and 2 (Figure 3) show strains of the
two alternating distorted [OH] tetrahedra I and II. Within one
4
tetrahedron we observe four shorter O···O and two longer
O···O distances. The molecular packing of compound B dis-
plays an intermolecular hydrogen bonding system with slightly
shorter O···O distances (2.69 Å) compared to those in com-
pound 2.[ Similar packing structures via intermolecular hy-
drogen bonding can be observed for [Fe(CO) ] [(μ-
15]
3
2
SCH ) CHOH] and the carboxylic acid functionalized model
2
2
[21]
[
Fe(CO) ] [(μ-SCH ) CHCOOH].
Furthermore, intermo-
3
2
2 2
lecular hydrogen bonding involving nitrogen atoms are de-
scribed in some model complexes containing amino acid deriv-
atives as ligands.[22]
Figure 4. Torsion angle (OCap–Fe–Fe–COap) in complex 2. Hydrogen
atoms were omitted for clarity.
In contrast to [Fe(CO) ] [(μ-SCH ) CH ][23], complexes 1
3
2
2 2
2
and 2 exhibit torsion angles defined by the apical CO across
the Fe–Fe bond (OC –Fe–Fe–CO ) due to the presence of
ap
ap
sterically demanding CH OH substituents at the bridgehead
2
atoms. The torsion angle in complex 2 (11.2°) is larger than
that in complex 1 (8.2°), whereas the basal CO groups in both
complexes are almost eclipsed (see Figure 4). The influence
of the steric demand of the bridgehead toward the solid-state
structure of the Fe S (CO) moiety has also been described in
2
2
6
1
2
1
2
[
Fe(CO) ] [(μ-SCH ) CR R ] (R /R = Me/Me, Et/Et), where
3 2 2 2
1
2
the apical CO torsion angles are 6° (R /R = Me/Me) and 15.8°
1
2
[13]
(
R /R = Et/Et).
The smaller torsion angle in complexes 1
and 2 compared to that in [Fe(CO) ] [(μ-SCH ) CEt ] is due
3
2
2 2
2
to the less steric bulk of the CH OH compared to the Et sub-
2
stituents.
Figure 5. CVs. of complexes 1 (solid line) and 2 (dashed line) mea-
sured at 200 mV·s scan rate. The concentration of the complexes is
Electrochemical Properties in Absence of Acid
–1
1.0 mM.
Cyclic voltammograms (CVs.) of complexes 1 and 2 are
shown in Figure 5. Complexes 1 and 2 exhibit reversible cath-
+
odic peaks at E1/2 = –1.53 V and –1.49 V (vs. Fc/Fc ), respec- show irreversible oxidation events at +0.67 V and +0.58 V for
tively. An additional reduction event (1: –1.97, 2: –1.93 V) can complexes 1 and 2, respectively.
be seen at a potential more negative than that for the primary
reduction of the complexes. The oxidative parts of the CVs. 1 and 2 are assigned to two successive reduction steps, RS1
At a scan rate of 200 mV·s–1 the primary cathodic waves of
1
514
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© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 1512–1519

3 2 2 2 2 2
Influence of OH Groups in [Fe(CO) ] [(μ-ECH ) C(CH OH) ] (E = S, Se) Complexes
Figure 6. CVs. of complex 1 at 0.05, 0.2, 0.4, 1 and 2 V·s (top left), 1 at 5, 10, 20, 50 and 100 V·s–1 (top right), 2 a 0.05, 0.2, 0.4, 1 and 2
–
1
–1
–1
V·s (bottom left) and 2 at 5, 10, 20, 50 and 100 V·s (bottom right).
and RS2, with closely spaced individual standard reduction po- even at fast scan rates? Typically, chemical reactions ac-
tentials, E° and E° , respectively.
companying the electron-transfer processes result in stabilizing
the SOMO to a level comparable or lower than the Fermi level
of the electrode being necessary for the first electron-transfer
process. The second electron transfer from the electrode to the
stabilized SOMO will occur at the Fermi level required for the
first electron transfer to the LUMO of the neutral species.
Stated simply, two-electron cathodic wave is observed when
a structural change makes the transfer of a second electron
thermodynamically more favorable than, or comparable to the
first. The structural change, as it has been found for various
complexes of the type [Fe(CO) ] [(μ-ECH ) X] (E = S, Se; X
1
2
I
I
–
I
0
1
Fe Fe + e ↔ Fe Fe (E° , k ) (RS1)
1
s
I
0
–
0
0
2
Fe Fe + e ↔ Fe Fe (E° , k ) (RS2)
2
s
The kinetic parameters ks1 and ks2 are the heterogeneous
electron transfer rate constants for RS1 and RS2, respectively.
Thus, the reduction events at –1.97 V and –1.93 V for complex
1
and 2, respectively, should be due to daughter products of
follow-up reactions. It is likely that these chemical reactions
involve CO loss either from the anion or the dianion as it was
found for various diiron carbonyl complexes.
[
23,24]
3 2
2 2
The anodic
=
bridgehead group), includes: (i) elongation of the Fe–Fe
waves at +0.67 V and +0.58 V for complexes 1 and 2, respec-
bond, (ii) cleavage of one of the Fe–E bonds and (iii) rotation
I
I
II II
tively, are assigned to the oxidation of Fe Fe to Fe Fe . The
conclusion that the primary cathodic waves of complexes 1
and 2 correspond to both RS1 and RS2 is based on comparison
of the peak height with that of [Fe(CO) ] [(μ-SCH ) CH ],
of one Fe(CO) unit to allow orientation of one of its CO li-
3
gands into bridging or semi-bridging position to delocalize the
negative charge.[
6–8,24i]
Previous DFT calculations showed that
3
2
2 2
–1
2
[7,27]
the structural change can occur mainly on the anion
or on
which is closer to a one electron process at 200 mV·s scan
the dianion[ . The described rearrangements result in a ro-
tated structure with an open site, which is similar to the active
site in Hred state (Figure 7). Consequently, the two-electron
nature of the reduction waves of complexes 1 and 2 can be
explained by structural rearrangements most likely leading to
a structure similar to that depicted in Figure 7. However, the
24i]
rate:[8,25]
The peak heights of the cathodic waves of complexes
1
and 2 are almost twice the peak height of [Fe(CO) ] [(μ-
3 2
SCH ) CH ] under the same conditions (Figures S6 and S7).
2
2
2
In addition, the intensity of these reduction waves increases at
–
1
faster scan rates up to 100 V·s , while the events at more
negative potentials become less visible (Figure 6). By increas-
ing the scan rate wave-splitting is not observed for the primary
cathodic processes of the structural analogues [Fe(CO) ] [(μ-
3 2
–
1
1
2
1
2
reduction of complexes 1 and 2 even at 100 V·s scan rate SCH ) CR R ] (R /R = Me/Me, Et/Et, Bu/Et) of complexes
2 2
2
which implies that the second heterogeneous rate constant k
1 and 2 show two one-electron reduction waves: a quasi-re-
s
1
[24i,26]
is larger than, or similar to k .
versible event at approx. –1.6 V and an irreversible reduction
s
1
2
[13]
The question that arises now is: Why does the cathodic pro- at approx. –2.4 V (for R /R = Et/Et).
In other words, re-
cess of complexes 1 and 2 tend to be two-electron reduction placement of the alkyl bridgehead substituents in these com-
Z. Anorg. Allg. Chem. 2013, 1512–1519
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
1515

R. Trautwein, L. R. Almazahreh, H. Görls, W. Weigand
ARTICLE
plexes by CH OH as in complexes 1 and 2 results in altering be observed clearly at higher AcOH concentrations. Neverthe-
2
the cathodic process from one- into two-electron transfer. less, it is not the main task of our current study to investigate
Clearly, these findings reveal the influence of OH toward the these mechanistic details of acid reduction in case of complex
reduction mechanism.
2.
Figure 7. Proposed rotated structure of the reduced species obtained
by reduction of the neutral complex.
It has been reported that the model complex [Fe(CO) ] [(μ-
3
2
1,2-hydroquinonedithiolato)] and related structures were stabi-
lized in the neutral and the reduced forms via internal hydro-
gen bonding between the OH groups and the adjacent sulfur
atoms.[ However, this study does not show whether the pres-
ence of hydrogen bonding can switch the cathodic process
from one- into two-electron transfer or not, because the com-
plex [Fe(CO) ] [(μ-1,2-hydroquinonedithiolato)] and the un-
12]
3
2
substituted [Fe(CO) ] [(μ-1,2-benzenedithiolato)] exhibit a
3
2
two-electron cathodic wave. In the light of these findings, we
suggested that the driving force for rotated structure formation
upon reduction of complex 1 or 2 can be due to the hydrogen
bonding between the OH group and the inverted iron or the
chalcogen atom as shown in Figure 8. The hydrogen bondings
may also account for the less negative reduction potentials of
1
2
complexes 1 and 2 compared to [Fe(CO) ] [(μ-SCH ) CR R ]
3
2
2 2
1
2
(R /R = Me/Me, Et/Et, Bu/Et).
Figure 9. CVs. of complexes 1 (1.0 mM) (top) and 2 (1.0 mM) (bot-
tom) at various concentrations of AcOH.
Indeed, this catalytic reduction of AcOH by complex 1 is
similar to other systems, which show two-electron cathodic
waves in the absence of acid.[
7,27]
A detailed catalytic
mechanism of AcOH reduction has been described for
[
27]
[
Fe(CO) ] [(μ-bdt)] (bdt = benzenedithiolato) as ECEC.
3 2
Therefore, we explain the catalytic reduction of AcOH by
Figure 8. Proposed hydrogen bonding in the reduced complexes 1 and complex 1 through ECEC mechanism in which the catalyst is
2.
–
the anion 1 (Scheme 3).
Electrocatalytic Proton Reduction
CVs. of complexes 1 and 2 in the presence of AcOH at
different concentrations show no increase in the current of the
two-electron cathodic waves, but suppression of the anodic
waves for the oxidation of the dianions. However, the catalytic
proton reduction waves are observed near –1.8 V and –1.9 V
for complexes 1 and 2, respectively (Figure 9). In case of com-
plex 2, it seems that there are two catalytic processes, process
I and process II, as shown in Figure 9. The catalytic current of
Scheme 3. Proposed ECEC mechanism for electrocatalytic reduction
process II increases faster than that of process I, which cannot of AcOH by complex 1.
1
516 www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 1512–1519

Influence of OH Groups in [Fe(CO)
3
]
2
[(μ-ECH
2
)
2
C(CH
2
OH)
2
] (E = S, Se) Complexes
and refined by full-matrix least square techniques against F
2
Conclusions
o
[
30]
(SHELXL-97 ). All hydrogen atoms were included at calculated po-
Model complexes 1 and 2 have been synthesized and char- sitions with fixed thermal parameters. All non-hydrogen atoms were
1
13
1
1
77
[30]
acterized by H, C{ H} and H Se HMBC NMR as well refined anisotropically.
XP (SIEMENS Analytical X-ray Instru-
ments, Inc.) was used for structure representations.
as IR spectroscopy, mass spectrometry, elemental analysis and
X-ray crystallography. The presence of sterically demanding
groups at the bridgehead of the complexes results in torsion
angle defined by the apical CO across the Fe–Fe bond. Re-
placement of the alkyl substituents in [Fe(CO) ] [(μ-
–
1
Crystal data for complex 1: C11
red-brown prism, size 0.06 ϫ 0.03 ϫ 0.03 mm, tetragonal, space group
I4 /a, a = 26.5730(4), b = 26.5730(4), c = 8.8956(1) Å, V =
281.40(15) Å , T = –140 °C, Z = 16, ρcalcd. = 1.887 g·cm ,
2 8 2 r
H10Fe O S , M = 446.012 g·mol ,
1
3
2
3
–3
6
1
2
1
2
[13]
SCH ) CR R ] (R /R = Me/Me, Et/Et, Bu/Et)
by CH OH
–1
2
2
2
α
μ(Mo-K ) = 21.49 cm , F(000) = 3584, 18960 reflections in h(–34/
substituents in complexes 1 and 2 alters the cathodic process 34), k(–34/25), l(–11/11), measured in the range 2.41° Յ Θ Յ 27.48°,
from one- into two-electron transfer. Moreover, the replace- completeness Θmax = 99.9%, 3602 independent reflections, Rint
ment of the alkyl groups by CH OH leads to lowering the 0.0435, 3295 reflections with F Ͼ 4σ(F
straints, R obs = 0.0356, wR obs = 0.0670, R all = 0.0414, wR all
=
2
o
o
), 208 parameters, 0 re-
1
2
1
2
=
reduction potentials. To explain these observations, we assume
that structural change occurs during the cathodic process lead-
ing to a rotated structure, which involves internal hydrogen
bonding between the OH group and the iron or the sulfur atom.
0
–
.0688, GOOF = 1.182, largest difference peak and hole: 0.594 /
0.433 e·Å .
–
3
= 539.802 g·mol–1,
2 8 2 r
Crystal data for complex 2: C11H10Fe O Se , M
brown prism, size 0.06 ϫ 0.06 ϫ 0.06 mm, tetragonal, space group
–
–
The anions 1 and 2 are the actual catalysts for the reduction
of AcOH. The substitution of sulfur by selenium in our com-
I4 /a, a = 26.9243(4), b = 26.9243(4), c = 8.9234(1) Å, V =
1
3
–3
plexes results in a longer Fe–Fe bond, smaller CO wave- 6468.73(15) Å , T = –140 °C, Z = 16, ρ
= 2.217 g·cm ,
calcd.
–
1
numbers and a higher overpotential concerning the catalytic μ (Mo-K
α
) = 63.3 cm , F(000) = 4160, 18984 reflections in h(–34/
reduction of AcOH.
24), k(–34/30), l(–11/11), measured in the range 2.40° Յ Θ Յ 27.48°,
completeness Θmax = 99.8%, 3711 independent reflections, Rint
.0392, 3394 reflections with F Ͼ 4σ(F
straints, R obs = 0.0315, wR obs = 0.0590, R all = 0.0373, wR all
=
=
0
o
o
), 210 parameters, 0 re-
1
2
1
2
Experimental Section
0
.0610, GOOF = 1.255, largest difference peak and hole: 0.526 /
–
3
All reactions were performed using standard Schlenk and vacuum-line –0.573 e·Å .
atmosphere. The 1H, C{ H}, and
13
1
1
H
77
Se
techniques under N
2
HMBC NMR spectra were recorded with Bruker Avance 200 MHz or
4
00 MHz spectrometer. Chemical shifts are given in parts per million
Synthesis of A [step (iii) in Scheme 2]
1
13
1
77
4 2
with reference to SiMe ( H, C) or to Me Se ( H Se HMBC). Mass
To a stirred solution of crude 8,8-dimethyl-7,9-dioxa-2,3-dithiaspiro-
spectra were recorded with a Finnigan MAT SSQ 710 instrument.
FTIR spectra were recorded with a Bruker Equinox 55 spectrometer
equipped with an ATR unit. Elemental analysis was performed with a
Leco CHNS-932 apparatus. Silica gel 60 (0.015–0.040 mm) was used
for column chromatography and TLC was performed using Merck
TLC aluminum sheets (Silica gel 60 F254). Chemicals were purchased
from Fisher Scientific, Aldrich or Acros and were used without further
purification. All solvents were dried and distilled prior to use accord-
[
2
4.5]decan prepared from (2.00 g, 6.62 mmol) 5,5-bis(bromomethyl)-
,2-dimethyl-1,3-dioxane in ethanol/water (30 mL/20 mL) was added
concentrated hydrochloric acid (1 mL). After stirring overnight at room
temperature most of the solvent was removed under reduced pressure
and the remaining aqueous phase was extracted five times with dichlo-
romethane. The combined organic phases were washed with water,
dried with sodium sulfate and the solvents evaporated to dryness.
[
15]
Crystallization from chloroform gave A (0.56 g, 3.37 mmol) in 52%
ing to standard methods. The starting material B
cording to literature procedures.
was prepared ac-
1
yield as slight yellow crystals. H NMR (400 MHz, [D
6
]DMSO,
3
3
2
4
4 °C): δ = 4.88 (t, JH,H = 5.4 Hz, 2 H, OH), 3.41 (d, JH,H = 5.2 Hz,
1
3
1
H, CH
2
OH), 2.90 (s, 4 H, SCH
OH), 58.69 (s, CCH
(166.262 g·mol ): C
2
). C{ H} NMR (101 MHz,
[
D
6
]DMSO, 24 °C): δ = 62.96 (s, CH
2
2
), 43.68 (s,
Electrochemistry
+
–1
SCH
2
). EI-MS: m/z = 166 [M] . C
5
H
10
O
2
S
2
Cyclic voltammetric measurements were conducted in three-electrode 36.15 (calcd. 36.12), H 6.06 (6.06), S 37.27 (38.57)%.
technique [glassy carbon disk (diameter = 1.6 mm), the working elec-
trode; reference electrode, Ag/AgCl in CH
the counter electrode] using a Reference 600 Potentiostat (Gamry In-
struments). All experiments were performed in CH CN solutions con-
taining 0.1 m Bu NBF at room temperature. The solutions were
purged with N for five minutes and a stream of N was maintained
3
CN; and a platinum wire,
General Procedure for the Synthesis of Complexes 1 and 2
3
Equimolar amounts of Fe
3
(CO)12 and either A or B were suspended
4
4
in toluene under N atmosphere and the resulting green suspension
2
2
2
was stirred for 1 h at 100 °C resulting in a color change to reddish
brown. After removal of the solvent under vacuum, the solid residue
was purified by column chromatography (dichloromethane/acetone 10/
over the solutions during the measurements. All potential values re-
+
ported in this paper are referenced to the potential of the Fc/Fc couple.
1) to afford complexes 1 and 2 as red and reddish brown solids, respec-
tively.
Crystal Structure Determination of Complexes 1 and 2
The intensity data were collected on a Nonius KappaCCD dif-
Complex 1: A (280 mg, 1.684 mmol) and Fe
3
(CO)12 (848 mg,
1
fractometer, using graphite-monochromated Mo-K
α
radiation. Data
1.684 mmol) in toluene (20 mL): 340 mg, 45%. H NMR (200 MHz,
3
were corrected for Lorentz and polarization effects, but not for absorp- [D
6
]acetone, 23 °C): δ = 4.05 (t, JH,H = 5.2 Hz, 2 H, OH), 3.39 (d,
tion.[
28,29]
.The structure was solved by direct methods (SHELXS
[30]
)
3
J
H,H = 4.9 Hz, 4 H, CH
OH), 2.38 (s, 4 H, SCH
). C{ H} NMR
13
1
2
2
Z. Anorg. Allg. Chem. 2013, 1512–1519
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de
1517

R. Trautwein, L. R. Almazahreh, H. Görls, W. Weigand
ARTICLE
(
4
(
6
3
C
50 MHz, [D
3.51 (s, CCH
υCO), 2001 (υCO), 1985 (υCO), 1980 (υCO), 1961 (υCO), 1075, 1025,
6
]acetone, 22 °C): δ = 208.85 (s, CO), 65.29 (s, CH
2
OH),
M. Rudolph, G. J. Vos, R. Tacke, W. Weigand, Inorg. Chem. 2010,
49, 10117–10132; b) U.-P. Apfel, Y. Halpin, H. Görls, G. J. Vos,
2
), 23.44 (s, SCH ). IR: 3278 (υOH), 2072 (υCO), 2022
2
W. Weigand, Eur. J. Inorg. Chem. 2011, 581–588; c) U.-P. Apfel,
H. Görls, G. A. N. Felton, D. H. Evans, R. S. Glass, D. L. Licht-
enberger, W. Weigand, Helv. Chim. Acta 2012, 95, 2168–2175.
7] M. K. Harb, J. Windhager, T. Niksch, H. Görls, T. Sakamoto,
E. R. Smith, R. S. Glass, D. L. Lichtenberger, D. H. Evans, M.
El-khateeb, W. Weigand, Tetrahedron 2012, 68, 10592–10599.
8] T. Liu, M. Y. Darensbourg, J. Am. Chem. Soc. 2007, 129, 7008–
–1
+
+
15, 561, 503 cm . DEI-MS: m/z = 418 [M–CO] , 390 [M–2CO] ,
+
+
+
+
62 [M–3CO] , 336 [M–4CO] , 306 [M–5CO] , 278 [M–6CO] .
[
–
1
11 2 8 2
H10Fe O S (446.012 g·mol ): C 29.76 (calcd. 29.62), H 2.39
(2.26), S 14.60 (14.38)%.
[
[
Complex 2: B (110 mg, 0.423 mmol) and Fe
0
[
3
3
(CO)12 (213 mg,
.423 mmol) in toluene (10 mL): 93 mg, 41%. H NMR (400 MHz,
7009.
1
9] J. S. McKennis, E. P. Kyba, Organometallics 1983, 2, 1249–1251.
3
D
6
]acetone, 27 °C): δ = 4.04 (t, JH,H = 5.0 Hz, 2 H, OH), 3.40 (d,
[10] a) W. Ziegler, H. Umland, U. Behrens, J. Organomet. Chem.
1988, 344, 235–247; b) M. T. Olsen, M. Bruschi, L. De Gioia,
T. B. Rauchfuss, S. R. Wilson, J. Am. Chem. Soc. 2008, 130,
77
2
JH,H = 4.8 Hz, 4 H, CH
2
OH), 2.44 (s with Se satellites,
J
Se,H
=
1
3
1
1
9.0 Hz, 4 H, SeCH
2
). C{ H} NMR (101 MHz, [D
6
]acetone, 24 °C):
OH), 42.80 (s, CCH ), 16.21 (s
). H 77Se HMBC NMR
]acetone, 24 °C): δ = 74.51 (s, SeCH ). IR:
307 (υOH), 2062 (υCO), 2013 (υCO), 1993 (υCO), 1972 (υCO), 1968
12021–12030; c) C.-H. Hsieh, Ö. F. Erdem, S. D. Harman, M. L.
δ = 209.71 (s, CO), 64.61 (s, CH
with 7 Se satellites, JSe,C = 83 Hz, SeCH
(
3
(
5
2
2
7
1
1
Singleton, E. Reijerse, W. Lubitz, C. V. Popescu, J. H. Reiben-
spies, S. M. Brothers, M. B. Hall, M. Y. Darensbourg, J. Am.
Chem. Soc. 2012, 134, 13089–13102.
2
400 MHz/76 MHz, [D
6
2
[
[
11] I. P. Georgakaki, L. M. Thomson, E. J. Lyon, M. B. Hall, M. Y.
Darensbourg, Coord. Chem. Rev. 2003, 255, 238–239.
12] J. Chen, A. K. Vannucci, C. A. Mebi, N. Okumura, S. C. Borow-
ski, M. Swenson, L. Tori Lockett, D. H. Evans, R. S. Glass, D. L.
Lichtenberger, Organometallics 2010, 29, 5330–5340.
13] M. L. Singleton, R. M. Jenkins, C. L. Klemashevich, M. Y. Dar-
ensbourg, C. R. Chim. 2008, 11, 861–874.
–
1
υCO), 1951 (υCO), 1075, 1025, 615, 561, 503 cm . DEI-MS: m/z =
+
+
+
+
12 [M–CO] , 484 [M–2CO] , 456 [M–3CO] , 428 [M–4CO] , 400
+
+
–1
[M–5CO] , 372 [M–6CO] .
C
11
H10Fe
2
O
8
Se
2
(539.802 g·mol )
·0.25C O: C 25.38 (calcd. 25.46), H 2.15 (2.09)%.
3 6
H
[
Crystallographic data (excluding structure factors) have been
deposited with the Cambridge Crystallographic Data Centre as [14] R. Gropeanu, M. Tintas, C. Pilon, M. Morin, L. Breau, R. Tur-
dean, I. Grosu, J. Heterocycl. Chem. 2007, 44, 521–527.
15] T. Niksch, H. Görls, M. Friedrich, R. Oilunkaniemi, R. Laitinen,
W. Weigand, Eur. J. Inorg. Chem. 2010, 74–94.
16] M. K. Harb, T. Niksch, J. Windhager, H. Görls, R. Holze, L. T.
Lockett, N. Okumura, D. H. Evans, R. S. Glass, D. L. Lichten-
berger, M. El-khateeb, W. Weigand, Organometallics 2009, 28,
supplementary publication CCDC-925461 for 1 and CCDC-925462 for
. Copies of the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [E-mail:
deposit@ccdc.cam.ac.uk].
[
[
2
Supporting Information (see footnote on the first page of this article):
IR spectra of complexes 1 and 2, additional cyclovoltammetric data,
molecular packing of 1 as well as depicted distances in the molecular
packing of 1 are shown in the Supporting Information.
1039–1048.
[
17] a) M. K. Harb, U.-P. Apfel, J. Kübel, H. Görls, G. A. N. Felton,
T. Sakamoto, D. H. Evans, R. S. Glass, D. L. Lichtenberger, M.
El-khateeb, W. Weigand, Organometallics 2009, 28, 6666–6675;
b) L.-C. Song, B. Gai, H.-T. Wang, Q.-M. Hu, J. Inorg. Biochem.
2
009, 103, 805–812.
Acknowledgments
[
18] a) Y. Nicolet, C. Piras, P. Legrand, C. E. Hatchikian, J. C. Fontec-
illa-Camps, Structure 1999, 7, 13–23; b) J. W. Peters, W. N. Lan-
zilotta, B. J. Lemon, L. C. Seefeldt, Science 1998, 282, 1853–
1858; c) Y. Nicolet, A. L. Lacey, X. Vernède, V. M. Fernandez,
E. C. Hatchikian, J. C. Fontecilla-Camps, J. Am. Chem. Soc.
L. A. thanks the Deutscher Akademischer Austausch Dienst (DAAD)
for scholarship. We are thankful to David Hornig for IR spectroscopic
investigations and Prof. Christian Robl for discussion.
2
001, 123, 1596–1601.
[
19] L.-C. Song, C.-G. Li, J. Gao, B.-S. Yin, X. Luo, X.-G. Zhang,
H.-L. Bao, Q.-M. Hu, Inorg. Chem. 2008, 47, 4545–4553.
20] a) U.-P. Apfel, Y. Halpin, H. Görls, G. J. Vos, W. Weigand, Eur.
J. Inorg. Chem. 2011, 581–588; b) U.-P. Apfel, H. Görls, G. A. N.
Felton, D. H. Evans, R. S. Glass, D. L. Lichtenberger, W. Wei-
gand, Helv. Chim. Acta 2012, 95, 2168–2175.
References
[
[
1] a) M. Frey, ChemBioChem 2002, 3, 153–160; b) R. Cammack,
Nature 1999, 397, 214–215; c) P. M. Vignais, B. Billoud, Chem.
Rev. 2007, 107, 4206–4272; d) J. C. Fontecilla-Camps, A. Vol-
beda, C. Cavazza, Y. Nicolet, Chem. Rev. 2007, 107, 4273–4303; [21] a) U.-P. Apfel, Y. Halpin, H. Görls, J. G. Vos, B. Schweizer, G.
e) A. L. De Lacey, V. M. Fernandez, M. Rousset, R. Cammack,
Chem. Rev. 2007, 107, 4304–4330.
2] Y. Nicolet, C. Piras, P. Legrand, C. E. Hatchikian, J. C. Fontecilla-
Camps, Structure 1999, 7,13–23.
3] J. W. Peters, W. N. Lanzilotta, B. J. Lemon, L. C. Seefeldt, Sci-
ence 1998, 282, 1853–1858.
4] a) C. Tard, C. Pickett, Chem. Rev. 2009, 109, 2245–2274; b) S.
Roy, S. Shinde, G. A. Hamilton, H. E. Hartnett, A. K. Jones, Eur.
J. Inorg. Chem. 2011, 1050–1055; b) W. Gao, L.-C. Song, B.-S.
Yin, H.-N. Zan, D.-F. Wang, H.-B. Song, Organometallics 2011,
Linti, W. Weigand, Chem. Biodivers. 2007, 4, 2138–2148; b) P. I.
Volkers, T. B. Rauchfuss, S. R. Wilson, Eur. J. Inorg. Chem. 2006,
4793–4799.
[
[
[
[22] a) U.-P. Apfel, C. R. Kowol, Y. Halpin, F. Kloss, J. Kübel, H.
Görls, J. G. Vos, B. K. Keppler, E. Morera, G. Lucente, W. Wei-
gand, J. Inorg. Biochem. 2009, 103, 1236–1244; b) X. De Hatten,
E. Bothe, K. Merz, I. Huc, N. Metzler-Nolte, Eur. J. Inorg. Chem.
2008, 4530–4537; c) C. He, M. Wang, X. Zhang, Z. Wang, C.
Chen, J. Liu, B. Åkermark, L. Sun, Angew. Chem. Int. Ed. 2004,
43, 3571–3574.
30, 4097–4107; c) G. Durgaprasad, R. Bolligarla, S. K. Das, J. [23] E. J. Lyon, I. P. Georgakaki, J. H. Reibenspies, M. Y. Dar-
Organomet. Chem. 2012, 706–707, 37–45; d) C. Topf, U. Mon-
kowius, G. Knör, Inorg. Chem. Commun. 2012, 21, 147–150.
5] a) Y. Nicolet, A. L. de Lacey, X. Vernede, V. M. Fernandez, E. C.
Hatchikian, J. C. Fontecilla-Camps, J. Am. Chem. Soc. 2001, 123,
ensbourg, J. Am. Chem. Soc. 2001, 123, 3268–3278.
[24] a) D. Chong, I. P. Georgakaki, R. Mejia-Rodriguez, J. Sanabria-
Chinchilla, M. P. Soriaga, M. Y. Darensbourg, Dalton Trans.
2003, 4158–4163; b) E. J. Lyon, I. P. Georgakaki, J. H. Reiben-
spies, M. Y. Darensbourg, Angew. Chem. Int. Ed. 1999, 38, 3178–
3180; c) X. Zhao, I. P. Georgakaki, M. L. Miller, R. Mejia-Rodri-
guez, C.-H. Chiang, M. Y. Darensbourg, Inorg. Chem. 2002, 41,
3917–3928; d) R. Mejia-Rodriguez, D. Chong, J. H. Reibenspies,
[
[
1596–1601; b) Y. Nicolet, B. J. Lemon, J. C. Fontecilla-Camps,
J. W. Peters, Trends Biochem. Sci. 2000, 25, 138–143.
6] a) U.-P. Apfel, D. Troegel, Y. Halpin, S. Tschierlei, U. Uhlemann,
H. Görls, M. Schmitt, J. Popp, P. Dunne, M. Venkatesan Coey,
1
518
www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 1512–1519

Influence of OH Groups in [Fe(CO)
3 2 2 2 2 2
] [(μ-ECH ) C(CH OH) ] (E = S, Se) Complexes
M. P. Soriaga, M. Y. Darensbourg, J. Am. Chem. Soc. 2004, 126, [26] a) J.-F. Capon, F. Gloaguen, P. Schollhammer, J. Talarmin, J.
1
2004–12014; e) J. W. Tye, J. Lee, H. W. Wang, R. Mejia-Rodri-
Electroanal. Chem. 2004, 566, 241–247; b) J. Windhager, M. Ru-
dolph, S. Bräutigam, H. Görls, W. Weigand, Eur. J. Inorg. Chem.
guez, J. H. Reibenspies, M. B. Hall, M. Y. Darensbourg, Inorg.
Chem. 2005, 44, 5550–5552; f) S. J. Borg, T. Behrsing, S. P. Best,
M. Razavet, X. Liu, C. J. Pickett, J. Am. Chem. Soc. 2004, 126,
2007, 2748–2760.
[
27] G. A. N. Felton, A. K. Vannucci, J. Chen, L. T. Lockett, N. Oku-
mura, B. J. Petro, U. I. Zakai, D. H. Evans, R. S. Glass, D. L.
Lichtenberger, J. Am. Chem. Soc. 2007, 129, 12521–12530.
28] COLLECT, Data Collection Software; Nonius B. V., Netherlands,
1
6988–16999; g) A. Darchen, H. Mousser, H. Patin, J. Chem.
Soc., Chem. Commun. 1988, 968–970; b) H. Mousser, Ph. D. The-
sis, University of Rennes, France, 1987; h) F. Robin, R. Rumin,
J. Talarmin, F. Y. Pétillon, K. W. Muir, Organometallics 1993, 12,
[
1998.
[29] “Processing of X-ray Diffraction Data Collected in Oscillation
Mode“”: Z. Otwinowski, W. Minor, in: Methods in Enzymology,
Vol. 276, Macromolecular Crystallography, Part A (Eds.: C. W.
Carter, R, M. Sweet), Academic Press 1997, pp. 307–326.
3
65–380; i) J.-F. Capon, S. Ezzaher, F. Gloaguen, F. Y. Pétillon,
P. Schollhammer, J. Talarmin, T. J. Davin, J. E. McGrady, K. W.
Muir, New J. Chem. 2007, 31, 2052–2064.
[
30] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
[
25] D. Chong, I. P. Georgakaki, R. Mejia-Rodriguez, J. Sanabria-
Chinchilla, M. P. Soriaga, M. Y. Darensbourg, Dalton Trans.
Received: February 21, 2013
Published Online: April 11, 2013
2003, 4158–4163.
Z. Anorg. Allg. Chem. 2013, 1512–1519
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
1519